The invention relates to making a fiber structure by multilayer weaving, and more particularly a fiber structure including at least one hollow portion, in particular a portion that is tubular or substantially tubular.
The field of application is in particular that of making fiber structures for use in providing fiber preforms for composite material parts that are obtained by densifying fiber preforms with a matrix, or parts that are obtained by hot isostatic pressing or by forging and diffusion-welding preforms made of metallic fibers, and particularly, but not exclusively, parts for aviation turbine engines. Examples include:                parts having at least one tubular portion secured to another portion such as a panel or a plate, the tubular portion being for enabling an element to be supported, guided, or hinged beside the panel; and        parts such as hollow support arms or ducts that may optionally be partitioned longitudinally in order to form a plurality of passages.        
Proposals have already been made to produce a fiber preform as a single piece from a multilayer woven structure in order to form a composite material part that is of complex shape.
The terms “multilayer weaving” or “three-dimensional weaving” are used herein to mean a weaving process between a plurality of layers of warp yarns and a set of weft yarns, at least some of the weft yarns interlinking warp yarns belonging to different layers of warp yarns. Several multilayer weaves can be used, such as interlock weaves, in which weft yarns in a given weft column move in the same manner in a plane of the weave, or else multi-satin, multi-plain, or multi-twill weaves. Reference may be made to Document WO 2006/136755.
It is known to make a multilayer woven structure that, on being shaped, makes it possible to obtain a preform having a shape that is close to the shape of a composite material part that is to be made. Reference may be made to Documents U.S. Pat. No. 7,241,112 and WO 2010/061139 that relate to making composite material blades for turbine engines.